Transmission of data over a low-bandwidth communication channel

ABSTRACT

Disclosed herein are various systems and methods that may improve the transmission of data over low-bandwidth communication channels in an electric power delivery system. Devices communicating across a low-bandwidth communication channel may implement several approaches, according to various embodiments disclosed herein, to reduce the data transmitted across the low-bandwidth communication channel and to prioritize the transmission of time-sensitive and/or more important information with respect to other data. Various embodiments disclosed herein may inspect packets to be transmitted across a low-bandwidth communication channel in order to identify high priority data. High priority data may be time-sensitive information, and accordingly, transmission of such data may be prioritized over other data in order to reduce transmission latency of the higher priority data.

TECHNICAL FIELD

This disclosure relates to systems and methods for managingcommunication between devices in an electric power generation anddelivery system, and more particularly, to systems and methods forimproving the transmission of data over low-bandwidth communicationchannels.

BRIEF DESCRIPTION OF THE DRAWINGS

Non-limiting and non-exhaustive embodiments of the disclosure aredescribed, including various embodiments of the disclosure withreference to the figures, in which:

FIG. 1 illustrates a simplified one-line diagram of an electric powerdelivery system and associated intelligent electronic devices (IEDs)consistent with certain embodiments disclosed herein.

FIG. 2 illustrates a conceptual timing diagram showing transmission ofmessages by an IED prior to and after a data state change consistentwith certain embodiments disclosed herein.

FIG. 3 illustrates a functional block diagram of an IED that may be usedto improve the transmission of data over a low-bandwidth communicationchannel consistent with certain embodiments disclosed herein.

FIG. 4 illustrates a block diagram of a data transmission system and thecalculation of transfer time of a message and a transmission time of amessage between a first device and a second device consistent withcertain embodiments disclosed herein.

FIG. 5 illustrates a block diagram of an Ethernet frame that mayencapsulate a GOOSE data packet consistent with certain embodimentsdisclosed herein.

FIG. 6 illustrates a functional block diagram of a system including atransmitting IED, a transmitting device, a receiving device, and areceiving IED consistent with embodiments disclosed herein.

FIG. 7 illustrates a flow chart of a method for transmitting a stream ofmessages over a low-bandwidth communication channel between stations inan electric power delivery system consistent with certain embodimentsdisclosed herein.

DETAILED DESCRIPTION

Electric power delivery systems may include electric power generation,transmission, and distribution equipment and loads that consume theelectric power. For example, such systems include various types ofequipment such as generators, transformers, circuit breakers, switches,distribution lines, transmission lines, buses, capacitor banks,reactors, loads, and the like. A purpose of electric power deliverysystems is to generate and deliver usable electric power to an end useror load. Often, the generation sites are located at great distances froman end user or load. Generated electric power is typically at arelatively low voltage, but is transformed into a relatively highvoltage before entering a transmission system. The voltage is againreduced for the distribution system, and often reduced yet again beforeultimate delivery to the end user or load. The electric power may bemonitored and controlled at various stages in the delivery system.Intelligent electronic devices (IEDs) are often used to collect electricpower system information, make control and/or protection decisions, takecontrol, automation, and/or protection actions, and/or monitor theelectric power delivery system.

IEDs within an electric power delivery system may be interconnected by avariety of technologies and may utilize various communication protocols.In some circumstances, IEDs may be connected via low-bandwidthcommunication channels, such as network radios. Low-bandwidth channelsmay create communication bottlenecks that result in delayed or lostmessages.

IEC 61850 GOOSE (Generic Object Oriented Substation Events) is aflexible method for signaling and data sharing over an Ethernet network;however, this flexibility may result in inefficient bandwidthutilization. Where the GOOSE protocol is used to communicate across alow-bandwidth communication channel, inherent redundancy in thecommunications protocol may tax an already limited communications linkbetween two devices in an electric power delivery system. Conventionalmethods to minimize impact on low-bandwidth channels include reducingthe size of the payload and or reducing the frequency of messagerepetition, These in turn cause a reduction in useable data beingtransmitted and longer time between messages which reduces the value ofits use as a channel heartbeat. As a result, GOOSE may perform poorlywhen implemented across a low-bandwidth channel, such as a radiocommunications channel.

Certain communication protocols, including GOOSE, may exacerbate datacommunications problems by transmitting multiple redundant copies of amessage. Transmitting the same or similar messages in a message streammay introduce a degree of dependability, helping to ensure thatsubscribing devices eventually receive messages. The increased networkload associated with transmitting a particular message multiple times,however, may cause communication bottlenecks, thereby causing certainmessages to be lost or delayed. IEDs may publish multi-cast messagesuntil data within the message payload changes. In certain embodiments, astate number associated with the message may represent a change in themessage payload, and an incrementing sequence number associated with themessage may indicate a number of messages that have been publishedreflecting a present data state. When the message payload changes (e.g.,a data state and/or a state change), the state number may be incrementedto reflect a new data state and the sequence number may be reset.

Some communications between IEDs, monitored equipment, and/or networkdevices may be more urgent and/or important than other communications.For example, control data or real time samples used in monitoring,controlling, automating, and/or protecting an electric power generationand delivery system or its components may be particularly valuable for acertain period of time. In other words, such values have a high timesensitivity, and if such time-sensitive data is not communicatedpromptly, its value may be diminished. Similarly, indications as to astate (e.g., a measured state) of one or more components and/orconditions within an electrical power generation and delivery system maybe important to communicate relatively contemporaneous with a data statechange event.

Disclosed herein are various systems and methods that may improve thetransmission of data over low-bandwidth communication channels in anelectric power delivery system. Systems and methods disclosed herein mayallow for communication between one or more stations (e.g., substationsand/or sets of IEDs, monitored equipment, and/or network devices) of anelectric power generation and delivery system that implement a varietyof communication protocols. Devices communicating across a low-bandwidthcommunication channel may implement several approaches, according tovarious embodiments disclosed herein, to reduce the data transmittedacross the low-bandwidth communication channel and to prioritize thetransmission of time-sensitive and/or more important information withrespect to other data.

Various embodiments disclosed herein may inspect packets to betransmitted across a low-bandwidth communication channel to identifyhigh priority data. High priority data may be time-sensitive informationand, accordingly, transmission of such data may be prioritized overother data to reduce transmission latency of the higher priority data.According to some embodiments, high priority data may compriseinformation relating to data state change events. Embodiments utilizingGOOSE may categorize a Boolean payload (e.g., “Permission”, “Block”,“Direct Trip”, etc.) as high priority data. Lower priority data maycomprise static data (e.g., an origin MAC address, a destination MACaddress, a VLAN tag, etc.). According to various embodiments, lowerpriority data may be encoded efficiently for transmission across thelow-bandwidth communication channel. Further, according to someembodiments, static lower priority data may be selectively omitted by atransmitting device and regenerated by a receiving device. Embodimentsutilizing GOOSE may categorize an analog payload, a priority tag, anEthertype field, and a reserved field as lower priority data. Inaddition to GOOSE, other embodiments of the present disclosure mayutilize communications protocols such as Sampled Values (SV),Manufacturing Messaging Specification (MMS), SEL Fast Message (FM),and/or Mirrored Bits®.

The embodiments of the disclosure will be best understood by referenceto the drawings, wherein like parts are designated by like numeralsthroughout. It will be readily understood that the components of thedisclosed embodiments, as generally described and illustrated in thefigures herein, could be arranged and designed in a wide variety ofdifferent configurations. Thus, the following detailed description ofthe embodiments of the systems and methods of the disclosure is notintended to limit the scope of the disclosure, as claimed, but is merelyrepresentative of possible embodiments of the disclosure. In addition,the steps of a method do not necessarily need to be executed in anyspecific order, or even sequentially, nor need the steps be executedonly once, unless otherwise specified.

In some cases, well-known features, structures or operations are notshown or described in detail. Furthermore, the described features,structures, or operations may be combined in any suitable manner in oneor more embodiments. It will also be readily understood that thecomponents of the embodiments as generally described and illustrated inthe figures herein could be arranged and designed in a wide variety ofdifferent configurations.

Several aspects of the embodiments described herein include softwaremodules or components. A software module or component may include anytype of computer instruction or computer executable code located withina memory device and/or transmitted as electronic signals over a systembus, a wired network, or a wireless network. A software module orcomponent may, for instance, comprise one or more physical or logicalblocks of computer instructions, which may be organized as a routine,program, object, component, data structure, etc., which performs one ormore tasks or implements particular abstract data types.

In certain embodiments, a particular software module or component maycomprise disparate instructions stored in different locations of amemory device, which together implement the described functionality ofthe module. A module or component may comprise a single instruction ormany instructions, and may be distributed over several different codesegments, among different programs, and across several memory devices.Some embodiments may be practiced in a distributed computing environmentwhere tasks are performed by a remote processing device linked through acommunications network. In a distributed computing environment, softwaremodules or components may be located in local and/or remote memorystorage devices. In addition, data being tied or rendered together in adatabase record may be resident in the same memory device, or acrossseveral memory devices, and may be linked together in fields of a recordin a database across a network.

Embodiments may be provided as a computer program product including anon-transitory machine-readable and/or computer-readable medium havingstored thereon instructions that may be used to program a computer (orother electronic device) to perform processes described herein. Themedium may include, but is not limited to, hard drives, floppydiskettes, optical disks, CD-ROMs, DVD-ROMs, ROMs, RAMs, EPROMs,EEPROMs, magnetic or optical cards, solid-state memory devices, or othertypes of media/machine-readable medium suitable for storing electronicinstructions.

FIG. 1 illustrates a simplified one-line diagram of an electric powerdelivery system 100 and associated IEDs 104, 106, 108, 115, and 170consistent with certain embodiments disclosed herein. System 100includes various substations and IEDs 104, 106, 108, 115, and 170configured to perform various functions. System 100 is provided forillustrative purposes and does not imply any specific arrangements orfunctions required of any particular IED. In some embodiments, IEDs 104,106, 108, 115, and 170 may be configured to monitor and communicateinformation, such as voltages, currents, equipment status, temperature,frequency, pressure, density, infrared absorption, radio-frequencyinformation, partial pressures, viscosity, speed, rotational velocity,mass, switch status, valve status, circuit breaker status, tap status,meter readings, and the like. Further, IEDs 104, 106, 108, 115, and 170may be configured to communicate calculations, such as phasors (whichmay or may not be synchronized as synchrophasors), events, faultdistances, differentials, impedances, reactances, frequency, and thelike. IEDs 104, 106, 108, 115, and 170 may also communicate settingsinformation, IED identification information, communications information,status information, alarm information, and the like. Information of thetypes listed above, or more generally, information about the status ofmonitored equipment, may be generally referred to herein as monitoredsystem data.

In certain embodiments, IEDs 104, 106, 108, 115, and 170 may issuecontrol instructions to the monitored equipment in order to controlvarious aspects relating to the monitored equipment. For example, an IED(e.g., IED 106) may be in communication with a circuit breaker (e.g.,breaker 152), and may be capable of sending an instruction to openand/or close the circuit breaker, thus connecting or disconnecting aportion of system 100. In another example, an IED may be incommunication with a recloser and capable of controlling reclosingoperations. In another example, an IED may be in communication with avoltage regulator and capable of instructing the voltage regulator totap up and/or down. Information of the types listed above, or moregenerally, information or instructions directing an IED or other deviceto perform a certain action, may be referred to as control instructions.

The electric power delivery system 100 illustrated in FIG. 1 may includea generation substation 111. Substation 111 may include generators 110and 112, which are connected to a bus 118 through step-up transformers120 and 122. Bus 118 may be connected to bus 126 in substation 119 viatransmission line 124. Although the equipment in substation 111 may bemonitored and/or controlled by various IEDs, only a single IED 104 isshown. IED 104 may be a transformer protection IED for transformer 120.IED 104 may receive a common time signal 186 which, as indicated below,may be distributed in system 100 using a communications network or usinga universal time source, such as GPS, or the like. Utilizing a common oruniversal time source may ensure that IEDs have a synchronized timesignal that can be used to generate time synchronized data, such assynchrophasors.

Substation 119 may include a generator 114, which may be a distributedgenerator, and which may be connected to bus 126 through step-uptransformer 118. Bus 126 may be connected to a distribution bus 132 viaa step-down transformer 130. Various distribution lines 136 and 134 maybe connected to distribution bus 132. Distribution line 136 may lead tosubstation 141 where the line is monitored and/or controlled using IED106, which may selectively open and close breaker 152. Load 140 may befed from distribution line 136. Further step-down transformer 144 may beused to step down a voltage for consumption by load 140.

Distribution line 134 may lead to substation 151, and deliver electricpower to bus 148. Bus 148 may also receive electric power fromdistributed generator 116 via transformer 150. Distribution line 158 maydeliver electric power from bus 148 to load 138, and may include furtherstep-down transformer 142. Circuit breaker 160 may be used toselectively connect bus 148 to distribution line 134. IED 108 may beused to monitor and/or control circuit breaker 160 as well asdistribution line 158.

A central IED 170 may be in communication with various IEDs 104, 106,108, and 115, using a data communications network. IEDs 104, 106, 108,and 115 may be remote from central IED 170. The remote IEDs 104, 106,108, and 115 may communicate over various media such as a directcommunication from IED 106, over a wide-area communications network 162,or using network radios 172 and 174. IEDs 104, 106, 108, 115, and 170may be communicatively linked together using a data communicationsnetwork, and may further be communicatively linked to a centralmonitoring system, such as a supervisory control and data acquisition(SCADA) system 182, an information system (IS) 190, and/or a wide areacontrol and situational awareness (WCSA) system 180. The datacommunications network among IEDs 104, 106, 108, 115, and 170 mayutilize a variety of network technologies, and may comprise networkdevices such as modems, routers, firewalls, virtual private networkservers, and the like, which are not shown in FIG. 1.

According to some embodiments, central IED 170 may be embodied as anautomation controller, a communications processor, and/or an informationprocessor. In various embodiments, central IED may be embodied as theSEL-2020, SEL-2030, SEL-2032, SEL-3332, SEL-3378, or SEL-3530 availablefrom Schweitzer Engineering Laboratories, Inc. of Pullman, Wash., andalso as described in U.S. Pat. Nos. 5,680,324, 7,630,863, and U.S.Patent Application Publication No. 2009/0254655, the entireties of whichare incorporated herein by reference. In certain embodiments, theautomation controller 150 and/or any other system illustrated in FIG. 1may be further communicatively coupled with one or more remote systemsor IEDs including, for example, a remote SCADA system 153 and/or aremote WCSA system 151 via one or more network devices 155, 157 and/orinterfaces.

The various IEDs in system 100 may obtain electric power informationfrom monitored equipment using potential transformers (PTs) for voltagemeasurements (e.g., potential transformer 156), current transformers(CTs) for current measurements (e.g., current transformer 154), and thelike. The PTs and CTs may include any device capable of providingoutputs that can be used by the IEDs to make potential and currentmeasurements, and may include traditional PTs and CTs, optical PTs andCTs, Rogowski coils, hall-effect sensors, and the like.

Each IED may be configured to access a common time source 186. Thecommon time source 186 may be distributed via a communications network(using, for example, IEEE-1588 protocol, NTP protocol, or the like), orobtained locally at each IED. The common time source 186 may be auniversal time, such as that delivered using global positioning system(GPS) satellites, WWVB, WWV, or the like. A common time may be used totime-synchronize measurements of the electric power system and/or in thecalculation of synchrophasors. Measurements may be paired with a timestamp or time tag indicating a time at which the measurement was made.Accordingly, phasors calculated by the IEDs may include a time stampindicating a time at which the measurement was made.

Central IED 170 may also be in communication with a number of otherdevices or systems. Such devices or systems may include, for example, aWCSA system 180, SCADA system 182, or local Human-Machine Interface(HMI) 187. Local HMI 187 may be used to change settings, issue controlinstructions, retrieve an event report, retrieve data, and the like. Insome embodiments, WCSA system 180 may receive and process thetime-aligned data, and may coordinate time synchronized control actionsat the highest level of the electrical power generation and deliverysystem 100. Mass storage device 184 may store data relating to system100 from IEDs 104, 106, 108, 115, and 170.

Central IED 170 may further include a time input, which may receive atime signal from a common time source 186. Time source 186 may also beused by central IED 170 for time stamping information and data. Timesynchronization may be helpful for data organization, real-timedecision-making, as well as post-event analysis. Time synchronizationmay further be applied to network communications. Time source 188 may beany time source that is an acceptable form of time synchronization,including, but not limited to, a voltage controlled temperaturecompensated crystal oscillator, Rubidium and Cesium oscillators with orwithout digital phase locked loops, microelectromechanical systems(MEMS) technology, which transfers the resonant circuits from theelectronic to the mechanical domains, or a global positioning system(GPS) receiver with time decoding. In the absence of a discrete timesource 188, central IED 170 may serve as a common time source bydistributing a time synchronization signal.

Data communications between IEDs 104, 106, 108, 115, and 170 may occurusing a variety of communication protocols, including GOOSE. Networkradios 172 and 174 may be configured to exchange messages betweencentral IED 170 and IED 115. As described above, GOOSE may performpoorly when implemented across a low-bandwidth communication channel,such as a radio communication channel. Accordingly, network radios 172and 174 may be configured to implement systems and methods disclosedherein for improving the transmission of data across a low-bandwidthchannel. According to one embodiment, network radios 172 and 174 may beconfigured to implement the systems and methods disclosed herein in away that is transparent to other devices in system 100, such as centralIED 170 and IED 115. In other words, network radios 172 and 174 maycommunicate with central IED 170 and IED 115 using the GOOSE protocol,but communication between network radios 172 and 174 may occur using analternative communication protocol that is transparent with regard toother devices in system 100. According to other embodiments, networkradios 172 and 174 may be integrated into central IED 170 and IED 115.

Information system 190 generally includes hardware and software toenable network communication, network security, user administration,Internet and intranet administration, remote network access and thelike. Information system 190 may generate information about the networkto maintain and sustain a reliable, quality, and secure communicationsnetwork by running real-time business logic on network security events,perform network diagnostics, optimize network performance, and the like.

FIG. 2 illustrates a conceptual timing diagram showing transmission ofmessages 200 and 204 by an IED prior to and after a data state changeconsistent with certain embodiments disclosed herein. The messages 200and 204 may be consistent with the GOOSE protocol. A message may includeone or more control instructions, monitored system data, communicationswith other IEDs, monitored equipment and/or other network devices,and/or any other relevant communication, message, or data. In certainembodiments, a message may provide an indication as to a state and/or adata state (e.g., a measured state) of one or more components and/orconditions within an electrical power generation and delivery system.For example, a message may provide an indication of a measured currentand/or voltage exceeding one or more thresholds. A certain state (e.g.,“Data State 1”) may be associated with a measurement not exceeding sucha threshold, while another state (e.g., “Data State 2”) may beassociated with a measurement exceeding a different threshold. A messageindicating a particular data state may be utilized to determine whetherthe measured current and/or voltage exceed the one or more thresholds.Similarly, a message may indicate a state of a component of an electricpower generation and delivery system, such as a state of a breaker(e.g., “open” or “closed”), a power storage device (e.g., “charged” or“depleted”), and/or the like.

A message may further indicate not only a particular data state, butalso whether the message indicates a data state that is different than adata state indicated by one or more preceding messages. That is, amessage may include an indication that data associated with the messagerepresents a data state change from a prior message. In certainembodiments, the prior message may be an immediately preceding message.Data state change information may be indicated by a data state changeindicator (DSCI) included in the message. For example, a DSCI includedin a message may be set to “1” following a first data state changeevent. According to some embodiments, the DSCI may be asserted in only afirst message following a state change event. In other embodiments, theDSCI may be asserted for a specified period of time or for a specifiednumber of messages (e.g., a message stream) following the data statechange event. The DSCI may be set to a different value upon a subsequentdata state change event. By utilizing a DSCI, a receiving device maydetermine that a particular message indicates a recent data state changewithout having to examine the contents (e.g., state information) of themessage and/or previously received messages.

In certain embodiments, an IED may transmit to subscribing (e.g.,receiving) devices and/or receive from publishing (e.g., transmitting)devices messages 200 reflecting a particular data state (e.g., “DataState 1”) at periodic intervals at a first communication rate after acertain period in which the state has remained constant. For example, ifa measured data state has not changed within the last 30 seconds, an IEDmay transmit messages 200 at periodic intervals at the firstcommunication rate. In certain embodiments, this periodic interval maybe relatively long, reflecting that a data state change has not recentlyoccurred. Transmitting the same or similar state messages periodicallyin a message stream may provide a way to monitor integrity of thecommunications network to ensure that subscribing devices maintainnetwork connectivity with the transmitting device. Further, thecontinuous transmission may serve as an indicator that the transmittingdevice is continuing to operate as expected. Accordingly, the continuousstream of messages may be referred to herein as a “heartbeat”.

Messages comprising redundant information regarding state may bedesignated with incrementing sequential numbers, as illustrated in FIG.2. As shown, messages 200 may increment their sequential numbers from 50to 53. Following the transition from state 1 to state 2, the firstmessage following the data state change even may have a sequentialnumber zero, which in subsequent messages may have an incrementallyhigher number.

When a data state change occurs (e.g., at 202), the IED may publishand/or receive messages 204 reflecting the changed state (e.g., “DataState 2”) at intervals having a second, typically variable,communication rate. As illustrated, in certain embodiments, the secondcommunication rate may be faster than the first communication rate.Accordingly, the period between sequential messages 204 may be shorterthan the period between sequential messages 200. As time progressesfollowing the data state change event 202, the communication rate of themessages 204 may progressively slow to reach, for example, a rate at ornear the first communication rate. In this manner, state messages may betransmitted at a relatively fast rate immediately following a data statechange event 202 that progressively slows as the data state change event202 becomes more remote in time. According to some embodiments, thetransmission rate may decrease exponentially for a period of timefollowing the data state change event 202.

Transmitting measured data state messages at a faster rate after a datastate change event 202 may help to ensure that devices subscribing tothe communications (e.g., subscribing IEDs) are more likely to receivethe messages indicating the data state change as closely as possible intime to the actual data state change event 202, since GOOSE is nativelya connectionless protocol. Transmitting redundant messages at arelatively fast rate, however, may introduce network congestion and/orbandwidth issues in some devices (e.g., communication switches, routers,radios, multiplexers, a real-time automation controller, IEDs, PLCs,and/or the like).

Retransmission of redundant messages may be particularly problematic inlow-bandwidth channels. Accordingly, redundant messages may be omittedby a transmitting device based on the status and sequence numbers. Areceiving device may regenerate the redundant messages in order tocomply with the GOOSE protocol.

FIG. 3 illustrates a functional block diagram of an IED 300 that may beused to improve the transmission of data over a low-bandwidthcommunication channel consistent with certain embodiments disclosedherein. Although FIG. 3 illustrates an IED that may be capable of avariety of functions (e.g., collecting electric power systeminformation, making control and/or protection decisions, implementingprotection actions, etc.), according to alternative embodimentsconsistent with the present disclosure, devices having significantlyless complexity and/or functionality may be utilized to implementsystems and methods disclosed herein. For example, the functionalitydisclosed herein for improving transmission of data across alow-bandwidth communication channel may be implemented by a networkradio, rather than a more complicated IED. IED 300 may be configured forbidirectional communication, and accordingly, may function as both atransmitting device and a receiving device.

IED 300 includes a communications interface 316 comprising a wiredinterface 340 and a radio interface 341. Communications interface 316may facilitate communication with one or more networks (not shown)utilizing either wired interface 340 and/or radio interface 341. Thenetwork may be in communication with other IEDs and/or system devices,and may therefore allow IED 300 to exchange information with suchdevices. In certain embodiments, the wired interface 340 may facilitatedirect communication with another IED or communicate with another IEDvia a network (not shown). IED 300 may further include a time input 312,which may be used to receive a time signal (e.g., a common or universaltime reference) allowing IED 300 to include a time-stamp oncommunications therefrom and/or synchronize sampling with other IEDs. Incertain embodiments, a common time reference may be received via networkcommunications interface 316, and accordingly, a distinct time input 312may not be required for time-stamping and/or synchronization operations.One such embodiment may employ the IEEE 1588 protocol. A monitoredequipment interface 308 may be configured to receive status informationfrom, and issue control instructions to, a piece of monitored equipment(such as a circuit breaker, conductor, transformer, or the like).

Processor 324 may be configured to process communications received vianetwork communications interface 316, a sensor component 310, time input312, and/or monitored equipment interface 308. Processor 324 may operateusing any number of processing rates and architectures. Processor 324may be configured to perform various algorithms and calculationsdescribed herein. Processor 324 may be embodied as a general purposeintegrated circuit, an application specific integrated circuit, afield-programmable gate array, and/or any other suitable programmablelogic device.

In certain embodiments, IED 300 may include sensor component 310, whichmay be configured to gather information relating to waveforms associatedwith an electric power delivery system. In the illustrated embodiment,sensor component 310 is configured to gather data directly from aconductor (not shown) and may use, for example, transformers 302 and 314and A/D converters 318 to sample and/or digitize filtered waveforms toform corresponding digitized current and voltage signals, which areprovided to bus 322. A/D converters 318 may include a single NDconverter or separate A/D converters for each incoming signal. A currentsignal may include separate current signals from each phase of athree-phase electric power system. ND converters 318 may be connected toprocessor 324 by way of bus 322, through which digitized representationsof current and voltage signals may be transmitted to processor 324. Invarious embodiments, the digitized current and voltage signals receivedvia sensor component 310 may be processed and stored oncomputer-readable storage medium 330 and/or transferred viacommunications interface 316 to an external mass storage device.

In some embodiments, IED 300 may also include contact input/output ports350. Contact input/output ports may comprise digital inputs/outputs 352and/or analog inputs/outputs 354. Contact input/output ports 350 maypermit direct communication with a variety of devices, such as tripsensors, intrusion systems, general failure alarms, etc., that providebinary information (e.g., open/closed, trip/no trip, alarm/no alarm). Inaddition to receiving binary signals, other types of data may also bereceived or transmitted via contact input/output ports 350. For example,a temperature sensor may be connected to contact input/output ports 350and may provide an indication of a temperature in a particular location.Further, contact input/output ports 350 may be associated with devicesthat are selectively enabled or disabled using contact input/outputports 350.

According to some embodiments, a device that does not communicateaccording to the GOOSE protocol may be directly connected to IED 300.IED 300 may generate a GOOSE message encapsulating the data generated bythe non-GOOSE enabled device. For example, an intrusion sensor may bedirectly coupled to one of digital inputs/outputs 352 and/or analoginputs/outputs 354. When the intrusion sensor is triggered (e.g., bydetecting that a door has been opened), a binary signal may begenerated. The binary signal may be converted by IED 300 into a GOOSEmessage that may be transmitted by either wired interface 340 or radiointerface 341.

A non-transitory computer-readable storage medium 330 may be therepository of various software modules configured to perform any of themethods described herein. A data bus 342 may link monitored equipmentinterface 308, time input 312, network communications interface 316, andcomputer-readable storage medium 330 to processor 324.

Protocol translation module 332 may be configured to allow IED 300 tocommunicate with any of a variety of external devices via networkcommunications interface 316. Protocol translation module 332 may beconfigured to communicate using a variety of data communicationprotocols (e.g., TCP/IP, IEC 61850, etc.). Further, protocol translationmodule 332 may be configured to translate data from one communicationsprotocol to another communications protocol in order to improvebandwidth utilization and/or decrease communication latency associatedwith certain higher priority data. According to some embodiments,protocol translation module 332 may be configured to generate a messagestream based upon signals received via contact input/output ports 350.As described above, such signals may be analog signals and/or digitalsignals. Such signals may be converted into a data protocol suitable fortransmission via wired interface 340 and/or radio interface 341.

Static data module 334 may be configured to optimize the transmission ofstatic data across a low-bandwidth communication channel. Variouscommunication protocols, including standard communication protocols andproprietary communication protocols may be utilized in variousembodiments consistent with the present disclosure. Examples of staticdata in a network utilizing the GOOSE protocol may include origin anddestination MAC addresses, VLAN and priority tags, Ethertype, andreserved fields. Static data may, according to some embodiments, bestripped by a transmitting device and re-created by a receiving device.For example, a network radio transmission system may incorporate a dataintegrity code. Accordingly, cyclical redundancy check (CRC) includedwith an Ethernet encapsulated GOOSE message may be redundant sincecorruption in the data may be detected using the network radiotransmission system's data integrity code. The CRC may therefore beremoved by a transmitting device and regenerated by a receiving device,according to certain embodiments consistent with the present disclosure.

GOOSE synchronism module 336 may maintain a replica at a receivingdevice, such as IED 300, of the static data of a given GOOSE publisherto which the receiver subscribes. Examples of this data include originand destination MAC addresses, VLAN and priority tags, Ethertype andreserved fields. As described above, the static data module 334 may omitfrom communication certain types of static data. In a receiving device,GOOSE synchronism module 336 may operate in conjunction with static datamodule 334 in a transmitting device to replicate a GOOSE message streamfrom the transmitting device.

As discussed above, GOOSE messages may also incorporate a plurality ofredundant messages, each of which may be designated by a state and asequential number. In order to reduce the bandwidth utilizationassociated with a GOOSE system, retransmission module 333 may beconfigured to omit redundant messages based on status and sequencenumbers in a message stream. According to some embodiments, anacknowledgment system may be implemented across the low-bandwidthchannel in order to ensure that a message relating to a change of statehas been successfully transmitted and received.

The retransmission pattern of redundant messages is not standardized inthe GOOSE protocol. Therefore, a receiving device, such as IED 300, mayfollow at least one of three approaches: (1) mimic the retransmit rateused by the transmitting device by generating redundant messages basedupon an abbreviated representation of a redundant message; (2)retransmit based on “time to live” parameters included in the GOOSEmessage stream meaning the data item in the GOOSE message itself thatinforms the receiving device about the maximum time a new message is tobe originated even if no new state occurs; (3) retransmit using aproprietary pattern. Each GOOSE message contains a “time to live” field,which informs the receiving device of the time that the next message isto be sent. Accordingly, the receiving device may determine when thenext packet is expected to arrive. Certain embodiments may utilize thefirst approach because it makes the conversion from GOOSE to a moreefficient protocol for transmission across the low-bandwidth channeltransparent; however, this approach may also have greater complexitywhen compared with the other two alternatives. According to otherembodiments, a system may send the redundant messages using an optimizedencoding for retransmission of redundant data. Any of the threeabove-described approaches may be implemented by retransmission module333.

Packet parsing module 338 may be configured to parse each message in astream of data packets and to identify higher priority data and lowerpriority data contained within each data packet. Higher priority datamay be transmitted as expeditiously as possible in order to minimize thelatency associated with such data. According to various transmissionprotocols, a data packet may comprise several types of data. These partsof the message may have different character, purpose and userapplication. In order to limit the bandwidth requirements and minimizetransmission latency, these parts may be identified and treatedappropriately. A specific example illustrated a block diagram of anEthernet frame encapsulating a GOOSE data packet consistent with certainembodiments disclosed herein is illustrated in FIG. 5. As shown in FIG.5, an Ethernet frame, for example, may comprise MAC addresses and otheridentifiers of the GOOSE publisher, sequence numbers, a Boolean payload,and an analog payload. MAC addresses and other identifiers of the GOOSEpublisher may be categorized as lower priority (or even static) data,and may be replaced by a simple and efficient identifier (e.g., anabbreviated representation) of a given GOOSE message to which thetransmitting device subscribes. This data may be transmittedperiodically at a relatively low rate, according to certain embodiments.In contrast, the Boolean payload of a GOOSE Ethernet frame may betreated as higher priority data, and may be transmitted immediately uponreceipt (e.g., in real-time or as near to real-time as possible).

Returning to a discussion of FIG. 3, data prioritization module 339 mayoperate in conjunction with packet parsing module 338 in order toprioritize the transmission of higher priority data. Data prioritizationmodule 339 may be configured to minimize the latency associated withhigher priority data. Similarly, lower priority data may be transmittedas capacity becomes available in the low-bandwidth communicationchannel.

Time module 335 may be configured to encode time information (e.g., atimestamp associated with a message) as efficiently as possible.Further, time module 335 may rely on an assumption that time will driftslowly between a transmitting device and a receiving device. Thisassumption is especially true in embodiments in which each transmittingdevice and each receiving device receive a common time signal (e.g., atime signal from the GPS system). According to one embodiment, the timeinformation may be transmitted according to a fixed schedule oravailability of capacity in the low-bandwidth communication channel inorder to limit drift between a transmitting device and a receivingdevice. According to another embodiment, a relatively short data valuemay represent an increment of time elapsed from a previously transmittedtime value.

As described above, status and sequence identifiers may be associatedwith a plurality of redundant packets transmitted according to the GOOSEprotocol. In order to conserve bandwidth, status and sequenceidentifiers may be generated or incremented by that receiving device.Similar to a time stamp included by time module 335, an abbreviatedrepresentation of the status and/or sequence identifiers may beexchanged frequently, while the full values of the sequence and statusnumbers are synchronized using a reduced transmission rate.

Status and sequence module 337 may be configured to generate orincrement at a receiving device status and sequence numbers associatedwith a message stream. Similar to the approach described above inconnection with time stamp module 335, an abbreviated representation ofa status number or a sequence number may be exchanged, while the fullvalues of the sequence and status numbers may be synchronized onlyperiodically or as capacity becomes available in the low-bandwidthcommunication channel.

FIG. 4 illustrates a block diagram of a data transmission system 400 andthe calculation of a transfer time of a message 430 and a transmissiontime of the message 430 between a first device 410 and a second device420 consistent with certain embodiments disclosed herein. Asillustrated, the first device 410 comprises a communications interface412 and a communication processing module 414. Similarly, the seconddevice 420 comprises a communication interface 422 and a communicationprocessing module 424. A message 430 is to be transmitted from the firstdevice 410 to the second device 420.

Calculation of the transfer time begins at 440, after message 430 hasbeen received via communication interface 412 and made available tocommunication processing module 414. Communication processing module 414may translate message 430 into an alternative protocol for transmission.For example, communication processing module 414 may convert message 430from a GOOSE format to an alternative format for transmission to thesecond device 420. The time between point 440, and the time that message430 is transmitted by the first device 410 may be referred to as t_(a).The transmission time between the first device 410 and the second device420 may be referred to as t_(b). Message 430 may arrive atcommunications interface 422, and after a period of time t, may be madeavailable to communication processing module 424. The sum of t_(a),t_(b), and t_(c), may be referred to as a transmission time. A transfertime may include an additional time period, t_(d), associated with theprocessing of message 430 by communication processing module 424. Thesum of t_(a), t_(b), t_(c), and t_(d) may be referred to as a transfertime.

The systems and methods disclosed herein are aimed at reducing the t_(b)time by considerably reducing the amount of data to be actually sent fortime sensitive messages. This in turn may result in increasedcomputational demands associated with communication processing module414 and 424. In other words, the scarce resource of communicationschannel bandwidth is traded for computational resources within the IEDsthat may be scaled up as much as required to implement the embodiments.

FIG. 5 illustrates a block diagram of an Ethernet frame 500 that mayencapsulate a GOOSE data packet consistent with certain embodimentsdisclosed herein. The frame starts with a preamble 502, which mayprovide a synchronization of the frame reception portions of receivingphysical layers with the incoming bit stream. A destination MAC address504 may identify the destination, and a source MAC address 506 mayidentify the sender. A link layer control field 508, which according tothe illustrated embodiment operates according to the 802.1Q standard,may control data traffic between devices sharing the same transmissionmedium. A type/length field 510 may comprise a code indicating aprotocol type according to which data and pad field 512 may beformatted. Where a transmitting and receiving station are communicatingusing GOOSE, this value may be specified as an Ethertype value of 88-B8(hexadecimal format). Data and pad 512 comprise the data to betransmitted. Data and pad 512 may comprise a sequence of n bytes, wherein some embodiments 42≦n≦1496 bytes. In certain embodiments, the totalframe minimum may be 64 bytes, and the pad may contain extra data bytes,if necessary, to bring the frame length up to its minimum size.

As described above, several of the fields of Ethernet frame 500 maycomprise static data for redundant data that may be transmitted moreefficiently by using abbreviated coding. As described above, thedestination address 504, source address 506, and type/length 510 may beomitted entirely, or may be replaced by a more efficient codingaccording to various embodiments. Similarly, frame check 514 may beomitted in view of data verification mechanisms provided by networkradio systems. Further reductions may be realized by more efficientlycoding sequential numbers and time values embedded within the data andpad field 512.

FIG. 6 illustrates a functional block diagram of a system 600 thatincludes a transmitting IED 602, a transmitting device 606, a receivingdevice 620, and a receiving IED 632 consistent with embodimentsdisclosed herein. As illustrated, transmitting IED 602 and transmittingdevice 606 may be connected via an Ethernet network 604. Transmittingdevice 606 may comprise a radio transmission system. Transmitting device606 may, according to some embodiments, further comprise systems forreceiving information from and/or providing information to non-GOOSEaware devices. A receiving device 620 and receiving IED 632 may beconnected by an Ethernet network 630. Similarly, receiving device 620may be configured to communicate with certain non-GOOSE aware devices.Each of transmitting device 606 and receiving device 620 may comprise asub-set of the components described above in connection with FIG. 3.Returning to a discussion of FIG. 6, according to various embodimentsconsistent with the present disclosure, transmitting IED 602 maygenerate a stream of messages for transmission to receiving IED 632. Thestream of messages may be created according to a first communicationsprotocol, namely GOOSE. The stream of messages may be transmitted viaEthernet network 604 to transmitting device 606.

Transmitting device 606 may parse the incoming stream of messages toidentify higher priority data 612, lower priority data 610, and staticdata 608. Transmitting device 606 may translate the incoming data streaminto a second communications protocol in which the higher priority data612 is prioritized over the lower priority data 610 and the static data608. The second communications protocol may further improve theefficiency of the encoding associated with any of higher priority data612, lower priority data 610, and/or static data 608 utilizing varioustechniques disclosed herein. The second communications protocol maycomprise a proprietary communications protocol or a genericcommunications protocol optimized for transmission of data across alow-bandwidth communication channel.

Higher priority data 612 may be transmitted to receiving device 620using a real-time, or near-real time process. The real-time process mayhelp to minimize the transfer time associated with the transmission ofhigher priority data, which may include time-sensitive information.Lower priority data 610 and static data 608 may be transmitted fromtransmitting device 602 receiving device 620 using a GOOSE synchronismprocess, which is described above, in connection with FIG. 3. As alsodescribed above, the GOOSE synchronism process may be responsible forgenerating a plurality of redundant messages constituting a “heartbeat”signal. According to some embodiments, the “heartbeat” signal may bebased upon an abbreviated representation of a sequence numbertransmitted in the second message stream. The complete sequence numbermay also be periodically transmitted in the second message stream. Inaddition, one or more time stamps in the first data stream may beconverted to an abbreviated representation for transmission betweentransmitting device 606 and receiving device 620 in the second messagestream.

Receiving device 620 may generate a third message stream by translatingthe second message stream into the first communications protocol (e.g.,GOOSE). The third message stream may include higher priority data 626,lower priority data 624, and static data 622. According to someembodiments, the first message stream may differ from the third messagestream due to the prioritization of higher priority data. According tosome embodiments, individual data packets may be altered in thetransmission process from transmitting IED 602 to receiving IED 632,although the communications protocol is the same. In other words, thefirst message stream and the third message stream may comprise aplurality of distinct packets.

According to some embodiments, a non-GOOSE aware device 614 may be incommunication with transmitting device 606. Non-GOOSE aware device 614may comprise a trip sensor, an intrusion sensor, general failure alarm,a temperature sensor, and the like. Similarly, a non-GOOSE aware device634 may be in communication with receiving device 620. A signal may begenerated by non-GOOSE aware device 614 that is transmitted totransmitting device 606. For example, non-GOOSE aware device 614 maycomprise an intrusion sensor that generates an alarm signal when a dooris opened. The alarm signal may be transmitted to transmitting device606, which may in turn create a GOOSE message encapsulating anindication that an alarm signal has been generated by non-GOOSE awaredevice 614.

A GOOSE message encapsulating data received from non-GOOSE aware device614 may be transmitted to receiving device 620, which may determine whataction should be taken based upon the data transmitted by non-GOOSEaware device 614. The data may be transmitted to Ethernet network 630and receiving IED 632, and/or the data may be routed to non-GOOSE awaredevice 634. Continuing the example discussed above relating to an alarmsignal generated by non-GOOSE aware device 614, non-GOOSE aware device634 may comprise an audible alarm configured to sound when an intrusionis detected. Accordingly, receiving device 620 may generate a non-GOOSEsignal based upon the GOOSE message encapsulating data received fromnon-GOOSE aware device 614 and transmit the non-GOOSE signal tonon-GOOSE aware device 634. The non-GOOSE signal may comprise, forexample, an enable or activate signal that causes an audible alarm tosound. According to this example, data may be generated by non-GOOSEaware device 614 that is consumed by non-GOOSE aware device 634.Accordingly, system 600 may facilitate direct communication betweennon-GOOSE aware devices 614 and 634 using GOOSE without the interactionof transmitting IED 602 and receiving IED 632.

FIG. 7 illustrates a flow chart of a method 700 for transmitting astream of messages over a low-bandwidth communication channel betweenstations in an electric power delivery system consistent withembodiments disclosed herein. Method 700 may be implemented by atransmission device and a receiving device configured to communicateaccording to a first communication protocol. Method 700 may begin byreceiving a first message stream including a plurality of actual datapackets according to the first communication protocol, at 702. Eachmessage of the first message stream may be parsed, at 704, in order toidentify higher priority data and lower priority data contained withineach message, at 706.

A second stream of data may be generated that includes a secondplurality of packets according to a second communications protocol atthe higher priority data is prioritized over the lower priority data, at708. The second stream of messages may be transmitted over alow-bandwidth communication channel, at 710. A receiving device maygenerate a third message stream comprising a third plurality of packetsby reformatting the second message stream according to the first format,at 720.

While specific embodiments and applications of the disclosure have beenillustrated and described, it is to be understood that the disclosure isnot limited to the precise configuration and components disclosedherein. Various modifications, changes, and variations apparent to thoseof skill in the art may be made in the arrangement, operation, anddetails of the methods and systems of the disclosure without departingfrom the spirit and scope of the disclosure.

What is claimed is:
 1. A method for transmitting a stream of messageover a communication channel between stations in an electric powerdelivery system, comprising: receiving a first message stream accordingto a first communications protocol, the message stream comprising afirst plurality of individual data packets; parsing each message of thefirst message stream; identifying higher priority data and lowerpriority data contained within each data packet; generating a secondmessage stream comprising a second plurality of packets according to asecond communications protocol in which the higher priority data isprioritized over the lower priority data; transmitting the secondmessage stream over a communication channel; and generating a thirdmessage stream comprising a third plurality of packets by reformattingthe second message stream according to the first communicationsprotocol.
 2. The method of claim 1, wherein transmitting the secondmessage stream comprises transmitting the second message stream using anetwork radio.
 3. The method of claim 1, wherein generating the thirdmessage stream comprises ordering packets in the third message stream toreduce transmission latency of the higher priority data.
 4. The methodof claim 1, further comprising: generating an abbreviated representationof a time stamp associated with a data value comprised within the firstmessage stream; transmitting the abbreviated representation of the timestamp in the second data stream; and regenerating the time stampcomprised within the first message stream.
 5. The method of claim 4,further comprising inserting into the third message stream a regeneratedheartbeat signal based upon a heartbeat signal in the first messagestream.
 6. The method of claim 4, further comprising incrementing asequence number in the third message stream based upon an abbreviatedrepresentation of the sequence number transmitted in the second messagestream.
 7. The method of claim 6, further comprising periodicallytransmitting the sequence number in the second message stream.
 8. Themethod of claim 1, further comprising generating an abbreviatedrepresentation of a static data value comprised within the first messagestream; transmitting the abbreviated representation of the static datavalue in the second message stream; regenerating the static data valuein the third message stream based upon the abbreviated representation.9. The method of claim 1, wherein the higher priority data comprises oneof a Boolean payload and a data state change indicator.
 10. The methodof claim 1, wherein the lower priority data comprises one of an analogpayload, an origin MAC address, a destination MAC address, a VLAN tag,and a priority tag, an Ethertype field, and a reserved field.